As Election Day fast approaches, Democrat Shannon O'Brien and Republican Mitt Romney, the two leading candidates for governor, have received a windfall of contributions from Massachusetts business leaders, who are funneling tens of thousands of dollars toward the campaigns in an effort to swing the tight race.

Women business executives, in particular, are coming to the aid of O'Brien. In addition to writing checks furiously for the current state treasurer, they are recruiting New York Sen. Hillary Clinton to attend a stretch-run, Oct. 30 luncheon fund-raiser at the posh Fairmont Copley Plaza hotel.

Chiefs of Massachusetts' most prominent private equity, venture capital and consulting firms, as well as leaders of traditional businesses, meanwhile, have flocked to the side of Romney, supplementing the more than $3 million that the wealthy Belmont businessman loaned his campaign earlier this month.

Yet, as the money pours in, the flow has not drowned out nagging concerns about both candidates. For O'Brien, it's years spent on Beacon Hill. For Romney, it's the sense that he is rarely seen among local business executives.

Still, the last-minute push to raise money is going ahead full force, in particular in the O'Brien camp. Scheduled for Oct. 30 at the Fairmont Copley Plaza, the Hillary Clinton fund-raiser was organized by a cadre of high-powered, female business executives, including Barbara Lee, the politically active ex-wife of buyout king Thomas H. Lee. Not surprisingly, O'Brien's attraction is a combination of gender and experience, her supporters say.

"This is the first time one of my own could be governor. That is really exciting," said Sheryl Marshall, managing partner of Axxon Capital LLC, a Boston venture firm that targets female entrepreneurs for investment.

"In many ways, a lot of businesswomen see a lot of themselves in Shannon," added Mary Anne Marsh, a consultant with Boston's Dewey Square Associates and an O'Brien supporter. "Like her, they've worked hard, moved up the ladder and have tried to make a difference. They clearly believe she's going to fight for them."

But O'Brien, the state treasurer, also has attracted some of the biggest names in the Boston business community, who have given as much as the legally imposed $500 annual limit on contributions to a single candidate.

In addition to the women expected to be in attendance at the Clinton fund-raiser — the second O'Brien fund-raiser featuring a Clinton (the other one being an Oct. 10 event with Bill Clinton) — bigwigs who have written checks for O'Brien include Amos Hostetter, former chairman and chief executive of Continental Cable; Justin Morreale, the Bingham McCutchen LLP attorney who oversaw the auction of the Boston Red Sox; Joseph Tucci, EMC Corp.'s chief executive; and Charles Glovsky of State Street Research & Management Co.

Her alliance with venture capitalist Christopher Gabrieli, the lieutenant governor candidate, has also netted private-equity players, such as David Fialkow, co-founder of General Catalyst.

In raising that money, O'Brien also is taking advantage of connections she has made to business interests during her four years as treasurer. "Shannon is not a stranger to the business community," said Larry Rasky, a longtime Democratic consultant.

Romney, too, enjoys the benefits of being a known quantity to business leaders here. He enjoys broad financial support in the private-equity community as well as the high-tech industry.

But he also has recently garnered money from the likes of Wayne Budd, executive vice president and counsel of John Hancock Financial Services Inc.; Richard DeWolfe, former real estate executive and current Boston University trustee; Gary DiCamillo, former head of Polaroid Corp. and now chief executive of TAC Worldwide Cos.; and Jeremy Jacobs, owner of the Boston Bruins and the FleetCenter.

Although Romney has been able to turn to such high-powered executives in recent weeks, the influx of cash may conceal a narrower support within the broader business community than commonly accepted, campaign observers say.

"Romney is only a known commodity in certain segments," noted Rasky. "He's not active in the traditional organizations," such as Associated Industries of Massachusetts and the Greater Boston Chamber of Commerce.

A Romney supporter, instrumental in persuading the former Olympics chief to speak before the Greater Boston Chamber of Commerce, said he's chided the campaign for not getting Romney before groups where he could get his message across. That could be a critical difference in a close race for a Republican in a predominantly Democratic state.

Also hurting Romney is the campaign's negative tone. "It's disappointing that there is very little discussion of issues," said Alan Macdonald, executive director of the Massachusetts Business Roundtable.

Although the negative campaign climate has been created by both candidates, it has made it difficult for Romney to increase his familiarity to voters, business leaders said. Yet it hasn't closed the contribution spigot, as finance executives continue to give to Romney and attorneys and female executives help finance O'Brien, said George Pillsbury, director of the Massachusetts Money and Politics Project.

Perhaps the hottest ticket in town is for the Oct. 30 fund-raiser featuring Sen. Clinton. The tickets, which sell for between $125 and $500, are moving fast.